I had an 04' E450 box truck with a V10, like 185k miles. Engine ran strong but thirsty. I had heard that the earlier V10 had plug issues but never looked to far into it. When i changed out the plugs just to see if they needed it, i first blew out the "well" the best i could. Then i sprayed some WD around the plugs then i slightly tightened the plugs before removing them. No problem.
Only issue i ever had was when the engine temp was acting up and it cut off half the cylinders. I thought it was the guage so i picked up a new sending unit. Then i discovered that the 04' anyway only used an air sensor in the left bank. Three auto parts shops in my town and no one knew that. Even had one get a box with the right sensor number on the box and the wrong sensor inside, lol.
I agree that i would buy the truck and if the cab was that bad then replace the cab.